The Evidential Argument from the History of Science, Part 3: Reply to Rauser on Defining Metaphysical Naturalism

Randal Rauser really doesn’t like the argument from the history of science (AHS). After I refuted his initial objections to AHS, he seems to have abandoned those objections. Instead, he now takes issue with the definition of metaphysical naturalism itself, a point he makes over the course of no less than three separate, additional replies. (See here, here, and here.) According to Rauser, metaphysical naturalism “is a vacuous cipher that is consistent with belief in the existence of an interventionist God.”

At first glance, his new approach seems like a stroke of genius. If metaphysical naturalism is consistent with theism, then it’s impossible for literally anything to be evidence favoring naturalism over theism. And therefore one doesn’t have to get bogged down in messy, contingent issues about which hypothesis (i.e., naturalism or theism) best explains the data; indeed, one doesn’t even have to deal with tricky issues about what counts as evidence! Instead, one can play the sort of semantic games which give philosophy a bad name, in which empirical evidence isn’t important. One might ask, “But what about all those high-falutin’ philosophers, from both sides of the aisle, like Plantinga, Swinburne, Moreland, Draper, Schellenberg, and Smith (to name just a few) who think that metaphysical naturalism is a serious alternative to theism?” I guess Rauser would say that he knows better than they do; they simply (and quite literally) do not know what they are talking about.

This is, of course, absurd. Just as it is misguided for noncognitivists to try to deny that theism is an explanatory hypothesis (by denying that “God exists” expresses a proposition), it is equally a mistake to try to deny that metaphysical naturalism is an explanatory hypothesis (by claiming that metaphysical naturalism is consistent with theism). But I’m getting ahead of myself. Lest I be accused of offering an inductively incorrect argument from authority, I want to consider his arguments.

Since Rauser pins so much of his latest batch of replies on my definition of metaphysical naturalism, let us begin by reviewing the definitions I’ve used throughout our exchange. Following Paul Draper, I’ve offered the following definitions.

physical entity: the kind of entity studied by physicists or chemists. Examples of physical entities include atoms, molecules, gravitational fields, electromagnetic fields, etc.[1]causally reducible: X is causally reducible to Y just in case X’s causal powers are entirely explainable in terms of the causal powers of Y.[1]ontologically reducible: X is ontologically reducible to Y just in case X is nothing but a collection of Ys organized in a certain way.[1] natural entity: an entity which is either a physical entity or an entity that is ontologically or causally reducible to a physical entity.[1]nature: the spatio-temporal universe of natural entities.[1]supernatural person: a person that is not part of nature but can affect nature. Examples of supernatural persons include God, angels, Satan, demons, ghosts, etc.[1]metaphysical naturalism (hereafter, “N”): the hypothesis that the universe is a closed system, which means that nothing that is not part of the natural world affects it.theism (hereafter, “T”): the hypothesis that there exists an omnipotent, omniscient, and morally perfect person (God) who created the universe.

It is trivial to show, by substitution of synonyms for synonyms, that N contradicts T. According to T, God created the universe. Since God created the universe, God is not part of the universe. Furthermore, God’s act of creation of the universe is an act which, by definition, affects the universe. Therefore, T entails that a being (God) which is outside of the universe affected (created) the universe. Thus, T contradicts N, which denies the existence of any being that is not part of the natural world but somehow affects it.

1. Rauser begins by complaining that I failed to provide a definition of N: “Unfortunately, in his definitive list of definitions Lowder doesn’t provide a definition for metaphysical naturalism.” Rauser seems to have confused “definitive list of definitions” with “exhaustive list of definitions.” I provided the definition of N just a little bit farther down in the article, under the heading “Rival Explanatory Hypotheses.” I give there the same definition of N which I provide above. To his credit, however, Rauser attempts to reconstruct my definition of naturalism from the other terms. He arrives at a definition which, while not identical to my actual definition, isn’t horrible. (I will briefly address why I don’t care for his reconstruction at the end of this post.)

2. Next, he writes, “nature is defined in such a way that it encompasses whatever science describes in the future as either natural or in relationship with the natural.” As we have just seen from my actual definitions, however, this is an oversimplification. The phrase, “in relationship with the natural,” is ambiguous: it could include ontological reduction, causal reduction, or–here’s the important part–some other unspecified type of “relationship.” The definition of “natural entity” does not allow for any other type of relationship. But let’s put that aside. What, precisely, is the problem?

According to Rauser, “Lowder’s naturalism is consistent with science establishing the existence of a non-physical substance that interacts causally with the realm of nature.” And why is that a problem? Rauser writes that one such reason is that

it is possible that a future neuroscience may have reason to affirm the existence of a non-physical substance that interacts with the brain. In the same way that the existence of subatomic particles can be inferred from their effects, so it is conceivable that a soul could be inferred from its effects.

An entity is logically compatible with N if and only if either (a) it is a physical entity, or (b) it is ontologically or causally reducible to a physical entity. How, precisely, would a ‘soul’ be logically compatible with N? Rauser’s scientific ‘soul’ (hereafter, ‘shmoul’) cannot be ontologically reducible to one or more physical entities, since he says it is (or is made out of?) a “non-physical substance.” Thus, if a shmoul is compatible with N, that is because a shmoul is causally reducible to a physical entity. Is it? Is it an unembodied mind? For that matter, what are the causal powers of a shmoul? Can shmouls which are not somehow associated with a physical brain (i.e., ghosts) somehow affect physical entities? Can shmouls exist without a physical universe? Rauser says nothing about this. In ordinary English, however, a “soul” is not causally reducible to physical entities, i.e., a soul’s causal powers are not entirely explainable in terms of the causal powers of physical entities. So it’s hard to see how the existence of a “soul,” at least as that word is defined in ordinary English, could be consistent with N.

I want to emphasize that I don’t rule out the possibility of a future scientific discovery which could provide evidence for souls (or shmouls). If such evidence is discovered that would be evidence for T and against N. But then it follows from the probability calculus that the non-existence of souls is evidence for N and against T.

3.This same problem refutes Rauser’s argument that N is consistent with the existence of God.

So now we’ve identified that Lowder’s naturalism is consistent with the existence of an indefinite range of non-physical substances interacting in nature. Whether or not we can identify one of those substances as God from within scientific discourse is quite irrelevant. The point remains that Lowder’s naturalism is consistent with God interacting in the physical world.

Again, Rauser seems to have forgotten the role of “natural entity” in the list of definitions I provided earlier. Yes, N is consistent with the existence of natural entities which are not physical entities. Such entities, however, must be either ontologically or causally reducible to physical entities. The theistic God, however, is neither ontologically nor causally reducible to physical entities.

4. Similarly, this same problem refutes Rauser’s claim to have discovered a contradiction.

On the one hand, Lowder’s naturalism is open to the existence of non-physical substances causally interacting in the physical world. On the other hand, it categorically denies this. So which is it?

Again, Rauser seems to have forgotten the role of “natural entity.”

What About Abstract Objects?

Let’s move onto Randall’s article, “Prejudice Against Supernatural Persons.” He asks why metaphysical naturalists (in my sense of metaphysical naturalism) believe there are no supernatural beings, while being open to abstract objects? Draper answers this question well: “[W]hile our knowledge of nature may provide reason to believe that nothing is supernatural, it provides little basis for the further conclusion that nature is all there is.”[2] This is also why I don’t care for Rauser’s attempt at reconstructing my definition of metaphysical naturalism.

I want to revisit Rauser’s complaint that N, as I have defined it, is open-ended. Again, he writes, “Thus, nature is defined in such a way that it encompasses whatever science describes in the future as either natural or in relationship with the natural.” The worry seems to be that if physicists or chemists in the future were to suddenly start appealing to God or other supernatural persons in their theories, then, God or other supernatural persons would suddenly become physical entities, just by virtue of the fact that physicists or chemists have appealed to them.

I have two comments, one very minor and one substantive. The minor comment is that physicists and chemists do not today appeal to supernatural agents in their theories, so God and other supernatural persons are clearly not physical entities today. (Okay, I said that was a minor point.) The more substantive comment is this. One can easily revise and expand the definition of N as follows:

physical entity: an entity which is either (1) the kind of entity studied by physicists or chemists today; or (2) the kind of entity studied by physicists or chemists in the future, which has some sort of nomological or historical connection to the kinds of entities studied by physicists or chemists today.[3]

Thus, even if physicists or chemists of the future appeal to God in their theories, God would not be a physical entity because He “is not subject to laws relating him to atoms, fields, and the like, nor would he share any common origin with such entities.”[4]